(a) Field of the Invention
This invention relates to breathing apparatus of the type wherein breathing fluid is provided to a mask upon a demand evidenced by inhalation by the user of the mask.
(b) History of the Prior Art
In the prior art, demand type valves for use in conjunction with breathing masks have been provided which are responsive to inhalation by the mask user. In one type of such mask a flexible member in the form of a diaphragm moves in response to the reduced pressure created in the mask chamber upon inhalation and actuates a lever which in turn opens a breathing fluid supply valve. Such masks, as shown in the prior art customarily are provided with an independent exhaust valve which opens upon exhalation to permit the escape of gas exhaled by the mask user. The exhaled gas both moves the diaphragm to its normal position of rest and opens the independent exhaust valve.